Salt diffusion and distribution in meat studied by Na-23 nuclear magnetic resonance imaging and relaxometry

This study introduces the use of combined Na-23 magnetic resonance imaging (MRI) and Na-23 NMR relaxometry for the study of meat curing. The diffusion of sodium ions into the meat was measured using Na-23 MRI on a 1 kg meat sample brined in 10% w/w NaCl for 3-100 h. Calculations revealed a diffusion coefficient of 1 x 10(-5) cm(2)/s after 3 h of curing and subsequently decreasing to 8 x 10(-6) cm(2)/s at longer curing times, suggesting that changes occur in the microscopic structure of the meat during curing. The microscopic mobility and distribution of sodium was measured using Na-23 relaxometry. Two sodium populations were observed, and with increasing length of curing time the relaxation times of these changed, reflecting a salt-induced swelling and increase in myofibrillar pore sizes. Accordingly, the present study demonstrated that pore size and thereby salt-induced swelling in meat can be assessed using Na-23 relaxometry.

Relational time for systems of oscillators

Using an elementary example based on two simple harmonic oscillators, we show how a relational time may be defined that leads to an approximate Schrodinger dynamics for subsystems, with corrections leading to an intrinsic decoherence in the energy eigenstates of the subsystem.

Stress corrosion cracking and hydrogen diffusion in magnesium

Evaluation of recent data for hydrogen (H) diffusion in magnesium (Mg) yielded a new equation for the diffusion coefficient of H in Mg. This indicates that there can be significant H transport ahead of a stress corrosion crack in Mg at ambient temperature and that H may be involved in the mechanism of stress corrosion cracking in Mg.

A diffusion approach to approximating preservation probabilities for gene duplicates

Consider a haploid population and, within its genome, a gene whose presence is vital for the survival of any individual. Each copy of this gene is subject to mutations which destroy its function. Suppose one member of the population somehow acquires a duplicate copy of the gene, where the duplicate is fully linked to the original gene's locus. Preservation is said to occur if eventually the entire population consists of individuals descended from this one which initially carried the duplicate. The system is modelled by a finite state-space Markov process which in turn is approximated by a diffusion process, whence an explicit expression for the probability of preservation is derived. The event of preservation can be compared to the fixation of a selectively neutral gene variant initially present in a single individual, the probability of which is the reciprocal of the population size. For very weak mutation, this and the probability of preservation are equal, while as mutation becomes stronger, the preservation probability tends to double this reciprocal. This is in excellent agreement with simulation studies.

Evidence of altered prefrontal-thalamic circuitry in schizophrenia: An optimised diffusion MRI study

MRI diffusion tensor imaging (DTI), optimized for measuring the trace of the diffusion tensor, was used to investigate microstructural changes in the brains of 12 individuals with schizophrenia compared with 12 matched control subjects. To control for the effects of anatomic variation between subject groups, all participants' diffusion images were non-linearly registered to standard anatomical space. Significant statistical differences in mean diffusivity (MD) measures between the two groups were determined on a pixel-by-pixel basis, using Gaussian random field theory. We found significantly elevated MD measures within temporal, parietal and prefrontal cortical regions in the schizophrenia group (P > 0.001), especially within the medial frontal gyrus and anterior cingulate. The dorsal medial and anterior nucleus of the thalamus, including the caudate, also exhibited significantly increased MD in the schizophrenia group (P > 0.001). This study has shown for the first time that MD measures offer an alternative strategy for investigating altered prefrontal-thalamic circuitry in schizophrenia. (c) 2006 Elsevier Inc. All rights reserved.

NMR microscopy: A tool for measuring monomer diffusion in supercritical CO2

The diffusion of styrene into linear low density polyethylene in a solution of supercritical CO2 was investigated using NMR microimaging. For both pure styrene and styrene dissolved in supercritical CO2, the diffusion was found to follow Fickian kinetics. Supercritical CO2 was found to enhance the rate and extent of diffusion of styrene into the substrate by up to three times under the conditions of this investigation, compared to pure styrene. NMR imaging was used to measure the concentration profiles of the styrene penetrants in real time, and the results were fitted to a Fickian model for diffusion. At a CO2 pressure of 150 bar and temperature of 40 degrees C, the diffusion coefficient of a 30 wt-% solution of styrene into LLDPE was calculated to be 1 X 10(-11) m(2). s(-1). This is significantly faster than the diffusion coefficient measured for pure styrene diffusion at 40 degrees C (3 x 10(-12) m(2). s(-1)). The diffusion coefficients determined by gravimetric analysis were slightly higher than those determined by the imaging method. This was probably due to residual styrene and/or polystyrene adhering to the surface of the films in the gravimetric technique.

Anisotropy-based robust performance analysis of finite horizon linear discrete time varying systems

We consider a problem of robust performance analysis of linear discrete time varying systems on a bounded time interval. The system is represented in the state-space form. It is driven by a random input disturbance with imprecisely known probability distribution; this distributional uncertainty is described in terms of entropy. The worst-case performance of the system is quantified by its a-anisotropic norm. Computing the anisotropic norm is reduced to solving a set of difference Riccati and Lyapunov equations and a special form equation.

Stochastic delay differential equations for genetic regulatory networks

Time delay is an important aspect in the modelling of genetic regulation due to slow biochemical reactions such as gene transcription and translation, and protein diffusion between the cytosol and nucleus. In this paper we introduce a general mathematical formalism via stochastic delay differential equations for describing time delays in genetic regulatory networks. Based on recent developments with the delay stochastic simulation algorithm, the delay chemical masterequation and the delay reaction rate equation are developed for describing biological reactions with time delay, which leads to stochastic delay differential equations derived from the Langevin approach. Two simple genetic regulatory networks are used to study the impact of' intrinsic noise on the system dynamics where there are delays. (c) 2006 Elsevier B.V. All rights reserved.

Use of regression equation of peripheral pulse timing characteristics to predict hypertension in children

Studies have shown that an increase in arterial stiffening can indicate the presence of cardiovascular diseases like hypertension. Current gold standard in clinical practice is by measuring the blood pressure of patients using a mercury sphygmomanometer. However, the nature of this technique is not suitable for prolonged monitoring. It has been established that pulse wave velocity is a direct measure of arterial stiffening. However, its usefulness is hampered by the absence of techniques to estimate it non-invasively. Pulse transit time (PTT) is a simple and non-intrusive method derived from pulse wave velocity. It has shown its capability in childhood respiratory sleep studies. Recently, regression equations that can predict PTT values for healthy Caucasian children were formulated. However, its usefulness to identify hypertensive children based on mean PTT values has not been investigated. This was a continual study where 3 more Caucasian male children with known clinical hypertension were recruited. Results indicated that the PTT predictive equations are able to identify hypertensive children from their normal counterparts in a significant manner (p < 0.05). Hence, PTT can be a useful diagnostic tool in identifying hypertension in children and shows potential to be a non-invasive continual monitor for arterial stiffening.